Why do ALL the vendors routinely & mindlessly add SIP ALG to their routers

[TTCP]

It seems that the SIP ALG feature is never useful, and in fact always causes problem. Then why do ALL the router vendors in the world routinely, mindlessly, stubbornly and tirelessly add this (mis-)feature to ALL of their router products, day after day, year after year?

Who in the world really benefits from using this SIP ALG feature in a router?

Are these engineers from the router vendors never reading Internet forum posts? Aren't they aware of all the complaints on SIP ALG feature all over the world?

Or is there any hidden agenda behind this act that cannot be disclosed to the general public?

[SteveInWA]

Great question.  I've never seen a use for SIP ALG.  It is a royal PITA to have to tell people to disable it.  At least most recent home routers come with the feature disabled, as it should be.

No hidden agenda; just a setting that costs the vendors nothing to continue supporting, for the few (commercial users)  who still use it.

[Mango]

Who in the world really benefits from using this SIP ALG feature in a router?

It can be useful if your service provider wants RTP (audio) to travel directly between you and the terminating carrier, or even you and the other party's phone.  However, I think all the different ways SIP ALGs are implemented defeats the purpose.  Making a switch work with every router out there would be a monumental (if not completely impossible) task.  Most service providers proxy all audio because even with SIP ALG, direct audio is just too damn hard to set up.